The present invention relates to a method and apparatus implementing the method for controlling the use of idle frames by a mobile station operating in a wireless telecommunications network. In the method, data transmission based on time division multiple access is divided into frames containing a fixed number of timeslots, and the frames are divided into timeslots containing bursts between the mobile station and a base transceiver station. The selected number of successive frames form the mobile station""s multiframe comprising traffic frames substantially intended for the transmission of traffic data, as well as idle frames intended for activities relating to the measurements of the radio path between the mobile station and a base station subsystem and the transfer of the measurement results.
Originally, digital cellular network systems have used circuit switched data transmission, whereupon a permanent transmission medium is provided for the time of the connection between the terminal equipments. Indeed, the data flow relating to speech transmission is reasonably continuous, whereupon circuit switched data transmission is normally effective enough as regards the utilisation of the radio resource. However, the data flow relating to data calls is typically bursty, in which case radio path is unnecessarily wasted on long-term reservation of timeslots for circuit switched data transmission.
Since it can be foreseen that the demand for data services in digital cellular network systems is growing rapidly, the European Telecommunications Standards Institute (ETSI) has launched preparations for standardising a new, GSM-based (Global System for Mobile Communications) packet switched data transmission service. The new service is known as the General Packet Radio Service (GPRS), and it has been developed to operate together with the traditional circuit switched GSM data transmission so that the radio path can effectively be utilised in connection with both data and speech transmission.
In the GSM system, communication between a mobile station (MS) and a base station subsystem (BSS) is implemented by transmitting data through a radio channel, the radio channel being made up of the timeslots reserved for the connection of the used radio frequency band. The GPRS provides an opportunity to dynamically adapt the capacity so that timeslots are only reserved for the connection when there is data to be transmitted, and the timeslots for data transmission directed from the mobile station to the base transceiver station and from the base transceiver station to the mobile station are defined separately. When data should be transmitted, the transmission of the data is faster due to the high capacity, and when there is no data to be transmitted, the capacity can be used for the needs of other connections.
The advantage of packet switched data transmission is substantially realised when a data transmission connection can be established quickly. If the establishment of a connection for transmitting a data packet is slow, a GPRS-type service for transmitting small-sized data packets is not justified. In order to quickly establish a connection in the GPRS system between the mobile station MS and a serving GPRS access point, a kind of virtual connection is established, in which case data transmission can be launched quickly if necessary without having to create or transmit all the data required for the establishment of the connection. For an optimum establishment and maintenance of said virtual connections, the mobile station should be able to continuously receive data from surrounding cells when transferring from one access point to another. This presupposes a kind of presynchronisation with the surrounding cells so that it is possible to transmit and receive the required cell data. The rate at which the mobile station is capable of being connected to a cell affects the establishment of the connection and, thus, the efficiency of the whole packet switched data transmission. Particularly in an urban environment, where there are a lot of surrounding cells and the mobile station has to monitor its environment at a rapid pace, it is important that the synchronisation is as fast as possible.
The intention of the present invention is to provide a method and apparatus implementing the method for enabling efficient utilisation of idle frames in wireless packet switched data transmission.
In a method, according to the invention, time division multiple access-based data transmission is divided into frames containing a fixed number of timeslots, and the frames are divided into timeslots containing bursts between a mobile station and a base transceiver station, and the selected number of successive frames form the mobile station""s multiframe, which comprises traffic frames substantially intended for the transmission of traffic data, as well as idle frames intended for activities relating to the measurements of the radio path between the mobile station and a base station subsystem and the transmission of the measurement results. It is characteristic of the method that the activities relating to the measurements of the radio path and the transmission of the measurement results, which can be carried out during an idle frame, as well as the operating mode of the mobile station are checked by the mobile station; the priority between the activities is determined according to the mobile station""s operating mode; and the operation having the highest priority is carried out by the mobile station during the idle frame.
Another objective of the invention is a mobile station, according to claim 5, for a wireless telecommunications system, wherein data transmission based on time division multiple access is divided into frames containing a fixed number of timeslots, and the frames are divided into timeslots containing bursts between the mobile station and a base transceiver station, and the selected number of successive frames form the mobile station""s multiframe, which comprises traffic frames substantially intended for the transmission of traffic data, as well as idle frames intended for activities relating to the measurements of the radio path between the mobile station and a base station subsystem and the transmission of the measurement results. It is characteristic of the method that the mobile station comprises means for checking the activities relating to the measurements of the radio path and the transmission of the measurement results, which can be carried out during an idle frame; for defining the mobile station""s operating mode; for defining the priority between the activities according to the mobile station""s operating mode; and for launching, during the idle frame, the operation having the highest priority.
The invention is based on the idea that the mobile station""s control unit comprises information about the activities that can be carried out during an idle frame according to the mobile station""s operating mode. At each idle frame, the mobile station checks said operating mode and the activities to be carried out and, from the activities to be carried out, determines the one having the highest priority on the basis of said operating mode. In a solution according to the invention, e.g. the number of idle frames used for searching for a synchronisation burst sent from a base station subsystem can be arranged by the mobile station as high as possible, whereby the probability that the timing burst and the mobile station""s said idle frame intended for the searching of the burst are synchronous is as high as possible.